First of All, LISTEN to what Christopher and others have already said, I'll echo it here but not as directly. It is imperative that you start with the basics and not worry about Mentalism until you know how to do (perform) traditional magic. As a parent however, I know you're not going to listen to such wisdom so here's the down low. . .
Start
here. . . at the back of the book you will find a list of chief study titles
The PDF I gave you the link to is FREE and will give you a far more complete overview as to what Mentalism is and isn't than most sources that have come out in the past decade or so. Understand too, that Mentalism is NOT the same as doing Magic; the psychology is completely different and too, Mentalism is very performance heavy -- you must be a solid showman and have excellent people management skills if you're to present good mentalism.
Traditionally the starter books that everyone will point you to are
13 Steps to Mentalism by Corinda and Annemann's
Practical Mental Magic. I'd add to this the Karl Fulve's
Self-Working Mentalism Effects text and Banachek's
Psychological Subtleties Vol 1 when it comes to foundation. I also have a FREE pdf that will soon be out, that deals with one of the most important secret weapons used in Mentalism -- The Swami (I'm very excited about this one in that I have contributions in it by some rather interesting VIP types like Lee Earle and Jeff McBride).
COLD READING is another skill you must cultivate in order to do effective Mentalism. If you follow the link you will find another FREE PDF that gives you the ins & outs around said practice.
If you are young doing mentalism effectively can prove a challenge; depending on your age, claiming to be an "expert" in body language or NLP as many currently do, simply isn't believable and thus, you need to find a claim that works for your situation. As you will find in those books, I encourage you to use your own life and family line as inspiration for creating your persona and claim. The more facts and truths you can sew into things, the better well received you will be and thus, the more prone your audience will be when it comes to believing you. Unlike traditional magic Mentalism requires belief and even solicits such -- disbelief is suspended. The problem is, so many have cheapened this side of things in recent years, by not paying attention to this factor.
Anywho, the two freebies will get you on your way and give you a huge list of resources, far more than anyone is going to expect you to ever go through.
Best of luck!